Contact microphone



Oct.`28, 1941. s. G. sEARs ErAL n 2,260,727

CONTACT MICROPHONE Filed July l2, 1938 2 Sheets-Sheet l Oct. 28, 1941. V s. G. SEARS ETAL 2,250,727

CONTACT YMICROPHONEA y 'Fi1ed.Ju1y 12, 1958 2 sheets-sheet 2 INV NTOR M man. M

Patented ct. 28, 1941 CONTACT MIonoHoNE e Sterling- G. Sears, Garden City, and William T.'

Weidenman, Sr., Spring Valley, N. Y., assignors to Telephonics Corporation, New corporation of New vYork York, N. Y.; a.'

Application July-12,1938, serial No. *218.728,*`

2 Claims.- (C1. 17g- 123) This invention relates to microphones and has particular reference vto microphones of the body contact type, whereby Vibrations of the voice are reproduced directly from the throat, cheeknor other-part of the body, forltelephone, radio or other uses. v Y I Body contact microphones, of `which the throat contact type has been'the most commonly used, have been cumbersome, inefficient-and so Variable in performance or poor in lreproducing quality as to be generally unsatisfactory. 4Nevertheless the body contact type microphone oiiers many advantages, providing its reproducing effectiveness and eciency could) be improved. Ofthe general'class of body( contact microphones, the throat type'offers particular advantages, although its position introduces the addition'al'objectiohs that the vibrations of the throat are 'deficient in high frequency response, 'and larefac'centuated in the lowfrequencies by reason of the natural resonance, of the vocal cords. vThusfthe prior' throat contact arrangements produce a distorted nasal quality, which, Vthough'j usually "j understandable with diiculty, require filters and the 'like forcorrecting ther deficiencies' in' reproduction. This necessity for 'filters andthe like ldisproportionately increases the sizeand 'cost'of the equipment.

actingA tothe vibrations, and relative movement between the electrodes with vconsequent reproductionresults.U Atwstill higher frequencies theinertia of one electrode y assembly.causesit, "in efnected electrodeY `vibrates at" considerable" am-v plitude inresponse Vto the vibrations.

In another; formY oi the` invention, the contact button is ydispensed with fand replaced by the entire casing, which'y is placed in contact with the throat orn'the like-for' bodily 'vibration thereby in response to speech.'l Th'e'microph'one element is resiliently suspended lin'ihebasirigV and the electrodes are each resilientl'yfsupported.for 'independent relative movement with'respe'ct to each other. Wtl'i this arrangement,th Weight of the casihg'is leeoi'.ivein suppre'ssrrgVibrations 0f large A`a'x'nplitiide andin transmitting Vibrations of higherifrequency to the modulating electrode. The inertia reaction 'respo'nse y of the microphone element "issubstantially the same' as was vdescribed in connection' With the contact button form. 'f

It will be seen `that the body `contact microphone of"this"invention` is very' eiiicient Vand effective for all purposes and hasparticular utility Where it is inconvenient if notv impossible to hold In accordance with the'present invention,"av

body contact microphone is provided, which' overcomes the objections vto the prior"devices: which efciently reproduces thedesirable Vibrations of the generating medium, such as the throat, head; chest, back, etc.; which effectively isolates the desirable vibrations from interference and 'undesirable vibrations; which produces substantially uniform vibrations over an. extended tone range without distortion due/to overloading and the like, and With a'quality comparing favorably with a direct speech or acoustic ymicrophone without the need of filters, and which is rugged, moisture-proof, light and comfortable to wear.

In a preferred embodiment of the body contact microphone of this invention, a reaction type carbon granule microphone element, having' relatively movable cooperating electrodes is movably suspended Within'V a casing held on the throat or other `speech-responsive portion of the body v'by suitable means, such as a flexible strap or band. In one form of the invention, a button connected to the element engages the throat for actuation by the speech vibrations. With this arrangement, the'responseof the element to low frequency vibration is small. while at higher frequencies the mass inertia'of the free parts of the Suspended element becomes more effective inrethe direct speech -oracousti'c "type of microphone before the lips,v suchas in an aeroplane, where the background noise level of AengineandY propel- 'ler vibration is high. Inasmuch as the "throat vibrations are the most diflicult toreproduce intelligibly,it follows that a body Contact microphone which is` eiectiveat that point will rbe at least as Aeiective in-reproducingvoice vibrations when in contact With-other voice-responsive parts of the body, -such as the cheek, head, chest, back and the like. v f f v V For a more completel understanding'of lthe invention,lreference may be had to the accompanying drawings, in which: v y 'Y Figure- 1 is an axial section through one form of the `body contactmicrophone ofthis inventj 0n;..f 5 N.

Fig. 2 is a cross-section through the micro- -phone 'as-seen Yalong 'the line 2--2 of Fig. 1, a portion of the .main Supporting VSpider beingvbroken away to illustrate the arrangement of the microphone element;A

. Fig. .3 is an axial section through another form of the invention, as seen along the line 3-3 of Fig. 4; Y z

Fig. 4 is a transversesection as seen along the -line 4--4 of Fig. 3, Va portion of the main supf porting ,spiderI being broken awayto illustrate the arrangement of the microphone element; and

Fig. 5 is a transverse section as seen along the line 5-5 of Fig. 3 illustrating the electrical contact arrangement on the interior of the back cover.

Referring to Fig. l of the drawings, numeral I designates a housing of suitable material, such as hard rubber, phenolic resin, metal, or the like, having a cap I I threaded thereon provided with a central aperture I2. Clamped between the cap I I and the bezel of the housing I0 is a spider I3, the

radial spokes I4 of which provide the spider with a degree of axial ilexibility. The spider I3 may have three spokes I4 and itfreelyjsupports the microphone element I5 within the housing I0 by means of a threaded stud I6'passing through the center of the spider I3, which is clamped between a nut I'I andanut I8 on the stud I6.-

The microphone element I5, thus floatingly mounted, comprises a casing I9, of insulating material such as hard rubber or the like, having an open front over which is'clamped the axially ilexible spider 2B and the flexible sealing gasket 2| by means of the clamp ring 22 threaded on the casing I9. The stud I6 which supports the microphone element I5 passes through spider 2i) and gasket 2| and is conveniently secured to the front electrode 23 within the microphone chamber 24 containing carbon granulesand a rear electrode 26 threaded on a nut 2'I in the rear of the casing I9. As shown inA Fig. 2, spider is provided with spokes, preferably three, andthe gasket 2| seals the Yspaces between them.

The nut 21 serves as a terminal for rear electrode 26'and is connected by a light flexible ribbonor wire 28 to one of the terminals 29 projecting through the housing IU, while' the front electrode 23 is electrically connected by stud I 6,' spider I3 and ribbon or wire 36 to the other terminal 28. The ribbon or wire 28 oiers no restraint tothe bodily movement of the microphone element within housing I0.

The stud I6 projects beyond theclampnut I8 through the center aperture I2 of the cap II Vand serves as a support for the applicatorbutton 3|, which is threaded thereon. Preferably interposed between the button'3l and the wall of the aperture I2 is a Aring 32 of felt, rubber, or thelike, which prevents the entrance of moisture or dust into housing I0. v i

For mounting the device on a helmetor other harness, a pair of clamp rings 33 are preferably threaded on the periphery of the cap II. If the microphone is tobe used for throat contact, for example, the rings 33 clamp the device on asuitable throat-encircling flexible bandvor strap 34 of leather', fabric, or the like. The band or strap 34 is fastened around the users rthroat so that vapplicator button 3| engages the flesh of the throat with sufficient pressure to effect intimate operative contact between the button 3| and the flesh. The usual point of contact with the throat is at the side toward'the front adjacent the-thyroid'cartilage, although other points on the throat and on the body may be utilized as desired, the intimacy of contact between the button 3| and the body part Ybeing essential, in each case.

In operation of the form of the contact microphone of this invention illustrated in Figs..1 and 2, the mere act of applying .the device to the body usually results in deflection of the spider I3 and a bodily. axial displacement of the microphone element I5 in the housing I0, due to the pressure of the applicator-button 3| .on the. body, the degree of such displacement being dependent upon the degree of the pressure. Usually this displacement is but slight, because too great pressure of the button 3| on the body will soon become uncomfortable. It will be observed that this bodily displacement of the microphone element I5 due to pressure on button 3| does not alter the relation between the electrodes 23 and 26, so that any degree of pressure on button 3| in use cannot aiect the performance of the microphone element I5 in its reproduction of the desired speech sounds. It will be understood that the microphone element I5 operates in the characteristic way of carbon granule microphones, in that the relative movement of the electrodes 23 and 26 rearrangesthe carbon granules 25 in chamber 24 so that the resistance to the flow of current between the electrodes is Varied in proportion to their movement, which in turn is in accordance with the speech vibrations.

VVery low frequency vibrations of the engaged body part in response to speech will cause the microphone element I5 to move substantially as a unit with little or no deflection of the inner spider 26, so that the relation between the electrodes 23 and 26 is not materially varied, with the result that little or vno sound is reproduced. This is particularly advantageous where the microphone is arranged. for throat use, since the vibrations of the throat are accentuated in the low frequencies, the 4major reproduction of which is undesirable.

When the vibration frequency is increased, the mass inertia of the casing I9, 'clamp ringl 22 and rear electrode 25 assembly becomes more effective in reacting to the vibrations ofthe button 3|, spiders I3 and A2|) and front electrodev 23 assembly. The' inertia ofthe formerassembly tends to cause it to remain stationary, so that `relative'rnovement betweenelectrodes '23 and 2,6 and consequent'reproduction of the speech takes place.

' At still higher frequencies, including the very high frequencies, the casing I9, clamp ring 22 and rear' electrode 26 assemblyV practically remains stationary due to its jinertia, with` the rcsult that the amplitude of movement' between the electrodes y23 and 26 isrelatively large vwith 'consequent reproduction ofthe speech vibrationsin accordance with their amplitude and frequency. Since the output' of' the microphone'element l5 is ingeneral proportional to the'displaceme'nt of the electrodes 23 and 26 with respect to each other, 4except for lthe characteristics of carbon contacts, the device of this invention has an output characteristic which rises with increase in frequency. This makes the device particularly adaptable for reproducing throat vibrations which are deficient in high frequency response, since the device reproduces the higher rfrequency vibrations eiiciently and suppresses or fails to respond efliciently to the over-accentuated low frequencies of the Vthroat vibrations.

Y In the form of the'invention illustrated in Figs. 3, 4 and 5, the applicator buttonof the arrangement of Fig. 1 is dispensed with and theentire housing Ill' takes its place, being. suitably supported 'byv a helmet, or harness such as a band-or strap for holding the front of the casing Il rin operative connection with the body part, Vsuch as the throat, head, chest, back, or any other body part which vibrates in response to speech of the user.. In thearrangement of Figsand 4 the microphone element I5 is, in effect, reversed, i, e., thespider I3 which supports it freely in housing interposed between spider I3 and clamp ring 36,`

both of which form part of the electrical circuit to be described. A stud lI6'v threaded into the center of the spider I3 and connected to the rear electrode 23 secures the microphone element I5 upon the spider I3', the'stud I6 passing through the axially flexible rear wall 20 of the element I5', which is clamped between the back of the rear electrode `23' and a nut I1' threaded on the stud I6 and I.serving as a spacer between spider I3 and wall 26.

The rear wall 20' is secured to the casing I9' of the microphoneelement I5 by a clamp ring 22 threaded on-the:l casing I9?. The opposite or front wall 38 `of fthe. microphone element I5 is likewise constituted by an axially flexible plate, secured in place by a clamp ring 39 threaded on .the casing I9' and mounting the front electrode 26' by means of a nut '40 threaded. on the stud. of the electrode 26. The: chamber 24 Within the microphone element I5' contains carbon granules 25 engaging the electrodes-23 and 26'. In the respect that both of its opposite electrode-bearing walls 23' Iand 38 are axially flexible, the arrangement of Fig. 3 differs from that of Fig. `1, in which only one such wall is flexible, namely 20, 2 I. The front and rear walls 38 and 26 may be imperforate, :axially flexible plates as shown in Fig. 4 or they may be spoked spiders similar to spider 26 of Fig. l with the spaces between their spokes closed by flexible sheet gaskets like 2|,in Fig. 1, depending upon requirements.

The electrical connections include a thin ilexible ribbon or wire 4I connected at one end to the nut 46 of front electrode 26 and extending through a groove 42 in the housing I0 to overlie the insulating gasket 31 for electrical engagement by the metal clamp ring 36. rIfhe rear electrode 23' is electrically connected to spider I3 through stud I6'. The rear of the housing I0 is closed by a cap 43 threaded into the rear opening thereof over a water-tight gasket 44. Preferably the cap- 43 is formed with an inclined conduit 45 into which the two-strand conductor 46 is watertightly sealed. The two strands 41 and 48' of the conductor are electrically connected to contact springs 49 and 50, respectively, which are secured to the under surface of the cap 43 and which are arranged to respectively engage the clamp ring 36 and spider I3', respectively, the former being connected to the front electrode 26 and the latter to the rear electrode 23'.- Connections between the microphone element I5 and the conductor 46 are accordingly simply completed by screwing the cap 43 in place.

In operation of the form of the invention exemplied by Figs. 3, 4 and 5, the device, suitably mounted on a helmet or harness, in a manner similar to that illustrated in Figs. 1 and 2, with the conductor 46 on the outside, engages the throat or other part of the body at the front surface of housing l with the intimate operative contact described. Thus applied to the body, there is no engagement between the body and the microphone element I', no matter what the pressure of the housing I0 on the body. The microphone element I5 being freely suspended in the' 'casing IUfb-y flexible spider I3" is accordingly afforded acertain freedom of bodily axial displacement, and is not submitted even tothe restraint affordedr by the applicator button 3| of thearrangement of Figs. 1 and 2. Also thereis no liability that the carbon will become electrically packed due to static pressures, and hence relatively inoperative. Y

As inthearrangement of Figs. 1 and 2, low frequencyfspeech 'vibrations applied to the housing I0 cause the microphone element I5' to oscillate bodily by reaction-.on spider I3 with little or no relative movement'between the electrodes 23 and 26. As thefrequency of .vibration is increased, the mass inertia of the microphoneelement casing I9 the clamprings22 and 39, front wall38 andpfront electrode 2.6 assembly causes it to react against the movement of the lighter rear wall 2D' and rear electrode 23 assembly, resulting in relative `movement between the electrodes 23' and 26 andconsequent reproduction of the speech. Likewise at. still higher -frequenciesthe inertia reaction'effect increases, the frontend assembly of the microphone element I5 in effect, remaining stationary. Theexible front wall 38, With the front electrode 26', provide a tunable element permitting further control rof the response range of the device, and enables the reinforcement or reduction of predetermined regions of the useful range. g In bothforms of the device the relative Weight of the microphone element I5 and I5- should be low and the stiifness ofthe springs I3, I3', 20, 26' and 38 shoul'dgbe relatively high, in order that' a long tone range may be effectively handled by the device. Thus, by a suitable selection of the stiffness of these Springs, and adjustmentof the mass or Weight of the microphone element I5 or I5', suitable variation in the response characteristic may be achieved for throat use. For example, the weight of the microphone element vI5' or I5 may be on the order of six grams, and the springs 20, 20' sufficiently stiff to cause the corresponding electrode resonance to be high in the frequency range to be reproduced. Similarly, springs I3, I3' should be relatively stiff so that the resonance thereof, Weighted by the microphone element I5, I5', will be at the top of the frequency range to be reproduced. Also to increase the inertia reaction eifect, housing I0 may be made heavier, as: by loading. l

A damping effect on the resonance of the springs is produced by the carbon granules in the microphone elements I5 and I5' and by the friction at the peripheries of the springs I3, 20, 20', 38. This friction damping may be increased if desired by interposing felt or other resilient material between the springs I3, 26, 20', or 38 and the corresponding engaging surfaces of the housing II), IIJ or casing I9, I9', as the case may be. This last expedient may be employed to increase the relatively low frequency response when the microphone is used on the head or cheek bone. Where the device is immediately over bone, a greater mass of the vibration responsive part of the device is permissible, since the bone effectively yattenuates the low frequencies.

It will be observed that in both forms of the device of this. invention, the electrodes 2'3, 26 and 23', 26 project Well into the carbon 25, 25', modu lating the material at approximately the center of the mass thereof, whereby the device is operative in all positions of use. Also, because the electrodes 23, 26 and 23', 26 are arranged for response movement in a direction parallel to the body vibrations, and as the extraneous vibrations due to propeller and exhaust noises, or engine or machine sounds are negligible in that direction, the device responds but little or not at all to such extraneous disturbances. Furthermore, the device is so constructed as to be effectively tunable to suppress the undesirable extraneous noises, thus reducing the background noise to) some thirty decibels below the average useful signal intensity, even under extreme conditions. Also,

if properly constructed of selected materials, the

device is unaffected by the high or 10W pressure or temperatures encountered in use.

Because the device of this invention maybe employed eiectively on any parts of the body which are responsive to local vibrations, it may be used as a stethoscope or the like, simply by adapting the response characteristic of the device toi the desired service. The device may also be employed for machinery vibration detection or analysis, and may be applied With varying pressure to any part without altering its sensitivity or causing the carbon to pack. While a carbon type microphone element has been illustrated and described herein, other forms of microphone element may be used With equal facility, providing only that it contains an electro-mechanical element which moves or vibrates in response to the sounds or vibrations to be reproduced to proportionally vary or eiect the development of an electrical current of proportional value. For eX- lample, an electromagnetic system With an air gap Variable by the vibration responsive movement of an armature in place of electrode 23 or 23, anda pole or poles in place of casing I or I9 and/or electrodes 26 or 26', or other equivalents of the ribbon or condenser type microphone elements and the like.

Y While certain preferred embodiments of the inventionrhave been yillustrated and described herein, it is tov be understood that the invention is not limited thereby, but is susceptible of changes in form and detail within the scope of the appended claims.

We claim:

1. In a body contacting microphone, the combination of a member adapted to be supported in operative connection with a voice-responsive body part for vibration thereby, a microphone element having opposite resilient Walls, spaced electrodes on said Walls, and resilient means in said member connected to one of said electrodes and supporting said element on said member for bodily movement relative to said member within at least part of the audible frequency range.

'2. In a body contact microphone, the combination of a member adapted to be supported in operative connection With a Voice-responsive body part for vibration thereby, a microphone element resiliently supported on said member and having opposite resilient Walls extending substantially parallel to the vibrating body part, and electrically-cooperating electrodes connected to said Walls for vibration thereby in response to vibration of said member by the body part for effecting corresponding electrical vibrations.

STERLING G. SEARS. W. T. WEIDENMAN, SR. 

